1. Technical Field
The invention relates to imaging systems and, particularly, to an imaging system and method for capturing a still image.
2. Description of Related Art
Referring to FIG. 4, ‘VD’ and ‘CCD exposure’ are timing lines of vertical sync pulses (VD) and charge coupled device (CCD) exposure amounts of CCD applications respectively. ‘Preview time’ and ‘Image capture time’ are periods before and after a final image is generated respectively. Generally, still image capture is categorized as high speed work, it typically involves exposing a CCD image sensor for an exposure time greatly shorter than a VD cycle time. This methodology almost always requires helps from special technologies. For example, referring to ‘Vsub’ timing line of FIG. 4, a high substrate voltage (Vsub) is used to clear CCD content, and thereby determine the exposure time, also known as electronic shutter technology. Additionally, referring to ‘Mechanical shutter’ and ‘Image data’ timing lines of FIG. 4, a mechanical shutter is used to block incoming light during a read image time, which is substantially successive to the exposure time in image capture time. In order to capture objects in motion and/or in bright light, an extremely short exposure time, e.g., 1/2000 s may be required. However, this raises two issues: (1) smear effect may be induced or aggravated in the CCD image sensor, since the degree of smear effect is inversely proportional to the exposure time; and (2) an extremely high-speed mechanical shutter is needed, which may be unachievable because mechanical devices have their speed limitation.
Therefore, it is desirable to provide an imaging system and a method for capturing a still image, which can overcome the above-mentioned problems.